staging: r8712u: Set device type to wlan

The latest version of NetworkManager does not recognize the device as wireless
without this change.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>